Project Summary/Abstract The gut microbiota consists of a complex microbial community that plays a number of important roles in human health, including protection from invading intestinal pathogens. Extracellular electron transfer (EET) describes a respiratory strategy that allows microbes to grow using electron acceptors exterior to the cell. I recently discovered a distinctive flavin-based extracellular electron transfer (FLEET) mechanism that is prevalent in gram-positive members of the gut microbiota, as well as the intestinal pathogens Listeria monocytogenes and multidrug-resistant Enterococcus faecalis. Traditionally viewed as a highly specialized growth strategy, the discovery of FLEET extends the relevance of EET into novel nutrient-rich environments, including within the complex microbial communities that define the gut microbiota. The studies proposed here seek to address: 1) the molecular basis of FLEET function, 2) determine the role of FLEET and associated respiratory mechanisms in the outgrowth of gram-positive pathogens in the gut, and 3) assess the effect of transferring high-energy electrons into the surrounding environment on gut microbial communities. Findings from these experiments promise to shape our understanding of interactions within microbial communities and metabolic strategies employed by gram-positive pathogens for intestinal outgrowth.